This invention relates to liquid insecticidal compositions whose active ingredients are a carbamate insecticide and a reaction product of the insecticide and formaldehyde or paraformaldehyde. The compositions contain only 1-35% by weight of water, thereby providing liquid compositions of solid insecticides having an unusually high concentration of active ingredients.
Insecticidal compositions of the carbamate insecticide methomyl and a reaction product of methomyl and formaldehyde are disclosed in U.S. Pat. No. 4,198,427 issued Apr. 15, 1980, to Buchanan. The patent further discloses that the compositions can be used in formulation with a water carrier, but only formulations having a relatively low concentration of active ingredients are discussed. Although these formulations are exceptionally effective insecticides, the low concentration of active ingredients requires high volume application. Additionally, although it is often desirable to prepackage and commercialize such compositions with water, compositions initially formulated to have greater than 35% by weight of water are often unstable at ambient temperatures in that methomyl can crystallize out of solution or, when ambient temperatures are low, the formulation can freeze. Crystallization of the carbamate can also occur upon diluting such formulations further with water, which can prevent proper distribution of the insecticide in the formulation and can clog spray nozzles during application of the formulation.
The present invention improves upon the compositions of U.S. Pat. No. 4,198,427 by providing a formulated composition having all the advantages of former compositions, such as effective insect control, and additionally being surprisingly stable at low temperatures and capable of dilution in all proportions without the occurrence of crystallization.